Mobile satellite communication systems (MSSs) providing global coverage are known. One such is the Iridium™ system, others are the ICO™ system the Globalstar System™, and the Teledesic™ system.
Since such systems operate globally (or at least, over a large part of the Earth's surface) they need to use a band of frequencies which are available all round the Earth.
Such MSS systems have inherent limitations in their capability to provide services to users who are indoors and are in dense urban areas. Thus the available frequencies for these systems are wasted in dense urban areas and indoors.
Various Terrestrial mobile communications providing local geographic coverage are know. Known systems include GSM and its variants, CDMA, IS-136 and a variety of others using time division multiple access (TDMA) and code division multiple access (CDMA) techniques.
Code division multiple access is a so-called “spread spectrum” system, in which a given mobile device communicates using a relatively wide band, produced by multiplying the digital signal with a high bit rate (“chip rate”) code sequence. Each code sequence defines a separate code channel.
Such systems, even though they are efficient and cost-effective in providing high capacity and coverage indoors and in dense urban areas, are not efficient and cost effective in terms of providing coverage to vast thinly populated rural areas.
Ideally, the satellite and terrestrial communications systems could be allocated completely separately frequency ranges, and they would then not interfere with each other.
Known systems like Iridium™ and Globalstar™ rely on roaming between satellite and terrestrial systems, and use completely different frequency spectrum for accessing the satellite and terrestrial systems. However, roaming between satellite and terrestrial systems would be a waste of valuable spectrum, considering that the spectrum used for Satellite communication system cannot be used in dense urban areas and indoors, while spectrum allocated for terrestrial use is not deployed in rural and ocean areas.
Accordingly, the present invention is designed to increase the possibilities for reusing the same channels (for example frequency channels) between terrestrial and satellite mobile communication systems.
U.S. Pat. No. 5,394,561 discloses a mechanism for networking satellite and terrestrial networks in which the power levels of the satellite and terrestrial communications are controlled so as to minimise co-channel interference.